1. Field of the Invention
This invention pertains to a method and apparatus for determining the level and dielectric constant of a liquid.
2. Description of the Prior Art
Various mechanical, electromechanical and sonic techniques have been employed to measure the level of a liquid or the interface levels between two or more liquids. The mechanical and electromechanical systems are relatively slow in reacting to changes in the level of the liquid while systems employing sonic or ultrasonic transmissions become complex when used to measure the surface levels of contained liquids because of echoes received from the surfaces forming the sides of the container.
Most prior art radiation reflection detection systems, while providing highly accurate indications of liquid level and responding in extremely short times to changes in the levels of the contained liquids, require very complex and expensive apparatus in order to function properly. A prior art system which minimizes this complexity and still provides the advantages of a radiation reflection detection scheme is disclosed in U.S. Pat. No. 3,832,900 issued Sept. 3, 1974 to the present inventor and assigned to the Sperry Rand Corporation. This invention utilizes an open coaxial line which is immersed in the contained liquid, the contained liquid thereby filling the coaxial line. The liquid surface creates a discontinuity in the coaxial line which produces a reflection of the baseband pulse signal that propagates back along the transmission line. The time at which this reflection is received, relative to the time of the transmitted pulse, determines the level of liquid. However, the transmission line tends to clog and requires frequent cleaning. The subject invention provides a method and apparatus for measuring the level of a liquid which eliminates the clogging problem, provides highly accurate level indications without the complexity of the prior art radiation reflection detection systems and determines the dielectric constant of the liquid.